With the coupled cpuidle driver (but probably also with other drivers),
a CPU loops in a temporary safe state while waiting for other CPUs of its
cluster to be ready to enter the coupled C-state. If an IRQ or a softirq
occurs, the CPU will stay in this internal loop if there is no need
to resched. The SCHED softirq clears the NOHZ and increases
nr_busy_cpus. If there is no need to resched, we will not call
set_cpu_sd_state_idle because of this internal loop in a cpuidle state.
We have to call set_cpu_sd_state_idle in tick_nohz_irq_exit which is used
to handle such situation.
Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
---
kernel/time/tick-sched.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index a402608..e19bbc9 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -526,6 +526,8 @@ void tick_nohz_irq_exit(void)
if (!ts->inidle)
return;
+ set_cpu_sd_state_idle();
+
__tick_nohz_idle_enter(ts);
}
--
1.7.10
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